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UBC Theses and Dissertations

Stability analysis and design for intelligent robot control Choi, Jooyeol

Abstract

This thesis focuses on the development and implementation of a robust and knowledge-based control approach for multi-link robot manipulator systems. A robot manipulator is a nonlinear and complex dynamic system that suffers from structured and unstructured uncertainties, and hence requires a robust control algorithm for satisfactory performance. Based on the concepts of sliding-mode control and fuzzy logic control (FLC), a fuzzy sliding-mode controller is developed, which possess good robustness properties of sliding-mode control and the flexibility and 'intelligent' capabilities of knowledge-based control through the use of fuzzy logic. The relationship between the design parameters of a fuzzy sliding-mode controller and the tracking performance of a closed-loop control system is established, so that a specification on tracking accuracy can be satisfied by proper choice of the controller parameters. To accommodate the control of a coupled system where the number of generalized coordinates that need to be controlled exceeds the number of control inputs, an alternative version of sliding-mode control termed coupled sliding-mode control, is introduced. Extensive simulation studies with both fuzzy sliding-mode control and conventional sliding-mode control are carried out for a single-module manipulator consisting of two links: one free to slew (revolute joint) while the other is permitted to deploy (prismatic joint). Furthermore, to represent the stability of a fuzzy logic control system rather comprehensively in terms of both qualitative and quantitative aspects, stability indices, which are measures of relative stability of a system, are established. These indices quantify the degree of variation to which a system can be subjected before becoming unstable. By considering the relationship between the stability indices and the design parameters, it is demonstrated that an FLC can be designed to guarantee global stability of a system. Also, using stability indices, a comprehensive stability analysis and design guidelines for coupled sliding-mode control are developed. Finally, the control schemes are implemented on a laboratory prototype of a variable-geometry manipulator. The experimental studies with fuzzy sliding-mode control as well as conventional sliding-mode control show that the tracking error is guaranteed to converge to a specification, which verifies the results obtained through analysis and computer simulations.

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